[Bennyboy71]

Nice little test you can do, courtesy of Sensaphonics:
 
http://www.sensaphonics.com/test/index.html

 

[DervishD]

Sometimes I perform another test to check seal and symmetric insertion: humming. Yes, I hum in a low voice. If I can hear my hum in the zone of deep basses and in perfect stereo, I have good seal in both ears and both ears have the same insertion depth. If the hum displaces to one ear or it is not deep bass enough, then I have to adjust.
 
I do this with new phones until I know how to adjust them in my ears using just my fingers.

 

[MusicalChillies]

I normally just clap my hands together and make funny noises